1. Field of the Invention
The present invention relates to a ring for a laminated type metal belt and a method for manufacturing the same, and in particular to a ring suitable for use as a metal belt element piece of a CVT (Continuously Variable Transmission) belt in a belt type CVT and a method for manufacturing the same.
2. Description of the Related Art
As well known, there is a trend where a metal-made CVT belt used as a transmission element of a belt type CVT is structured by connecting several hundreds of generally V-shaped metal blocks by an endless metal belt and a belt obtained by laminating thin plate-shape endless rings in several layers is used as the metal belt itself.
The above-mentioned ring is manufactured through not only a step where a coil member made of special steel such as maraging steel or the like is formed in an annular shape and it is connected at both end portions through welding to form a endless ring work material, a step where the ring work material is cut so as to have a predetermined width and a step where each of inner and outer corner peripheral edge portions of the cut ring work material is polished in a R chamfer shape while removing a burr generated at the time of cutting step, but also a rolling (plastic working) step, a heat treating step and the like.
A more specific process for cutting the ring is performed in the following manner. That is, a wide and endless ring work material is wound between a pair of rolls to be rotated around them while being applied with a predetermined tension. Meanwhile, a cutter is provided on one of the rollers coaxially therewith, and a cutter is provided on a pressing roll which is pressed to the one of the rollers. Then, the ring material is cut with shearing force between the cutters generated by applying a press force to the pressing roll and a ring with a predetermined width can be obtained.
In the above conventional manufacturing method, since a ring cutting method based on shearing is employed, it is impossible to avoid formation of a fracture surface on a sheared material face but also burr generation due to a special property of the method. Such a drawback factor as burr or the like can be removed to some extent by a polishing working at the subsequent step, but the burr may remain on the ring due to its size even after the polishing working. If the burr remains on the ring, there is a tendency that it acts as a trigger of ring damage, or the like due to metal fatigue or stress concentration so that the ring may be shortened.
Particularly, since a ring used in a CVT belt is circulated continuously between a pair of V-groove pulleys under an actually using state, a load acting on an outer peripheral side of the ring is larger than that acting on an inner peripheral side thereof, so that it is not allowable that the above drawback factor remains on the inner peripheral corner edges of the ring.
In view of the above, in the conventional art, it is assumed that a polishing work is performed on the outer peripheral corner edge portion of the ring and the inner peripheral corner edge portion thereof so as to form the same R chamfer shape, but it is necessary to perform the polishing working on the former and the latter independently in order to remove all of the drawback factors, which results in increase in manufacturing cost of the ring necessarily.
Also, when a cutting process where a ring is cut by cutting with whetstone instead of a shearing type cutter is employed, it is possible suppress generation of a drawback factor such as a burr largely. However, it is necessary to take in consideration a grinding margin corresponding to the width of the whetstone due to the special property of a whetstone in advance. As a result, material yield deteriorates extremely so that such a cutting process is not practical.
Also, when the whetstone is worn, it is necessary to replace it with another, which results in increase in manufacturing cost.
Furthermore, in a case that shearing of an endless ring is started at one point thereof and the shearing is performed over about one turn of the ring, when a portion of the endless ring which is positioned near to the one point and which has not been sheared yet is produced in a final stage where the shearing approaches to the one point, the portion is ruptured by a pressing force of the cutter. Accordingly, the fracture surface is formed over the entire fracture surface the portion of the ring which has not been sheared in the direction of the thickness. Furthermore, since the portion of the ring which is positioned near to the one point is plastically deformed by the pressing force of the cutter, deterioration of quality of the ring is caused.
The present invention has been achieved with such points in mind.
It therefore is an object of the present invention to provide a ring for a laminated type metal belt, whose life or durability is improved and a method which allows easy manufacture of the ring.
To perform the object, according to one aspect of the present invention, there is provided a ring for a laminated type metal belt which includes: an endless metal ring, the ring being for configuring a belt by laminating a plurality of the rings, wherein the ring is chamfered at each of its inner and outer peripheral corner edges; and the radius of curvature of the chamfered portion of the inner peripheral corner edge of the ring is set to be larger than the radius of curvature of the chamfered portion of the outer peripheral corner edge of the ring.
Another aspect is a method to manufacture a ring for a laminated type metal belt which includes the following steps: entraining a wide and endless ring work material between one roll provided with an indentation punch having an angle-shaped edge and anther roll to move the ring work material in a circulating manner; pressing a pressing roll on to the indentation punch so as to sandwich the ring work material; cutting the ring work material by indentation action of the indentation punch to obtain a ring with a predetermined width size; and performing a polishing working on inner and outer peripheral corner edge portions of the ring which has been cut. According the steps described above, the ring is chamfered at each of its inner and outer peripheral corner edges, and the radius of curvature of the chamfered portion of the inner peripheral corner edge of the ring is set to be larger than the radius of curvature of the chamfered portion of the outer peripheral corner edge of the ring.